1. Field of the Invention
The present invention relates to a tachograph having an external data input and to a method and system in which such a tachograph is used.
2. Description of Prior Art
Tachographs, particularly digital tachographs, must be installed in commercial vehicles according to EU regulations. Usually, these tachographs are equipped with a printer used to produce printouts that are required legally. In this case, the relevant data is conditioned by the tachograph and then made available to the printer as the output device.
The tachograph receives the data it requires via a data bus, what is known as a CAN bus. By way of example, the CAN bus has an onboard computer or a speed pulse generator, which is arranged on a camshaft, connected to it. The data ascertained by the aforementioned devices are then sent via the CAN bus to all devices arranged on the data bus using a previously defined protocol, wherein the receiving device recognizes the data packets which are intended for it from an encoding.
In the case of a bus structure, the devices are connected to one another permanently. In particular, it is difficult in the case of the CAN bus to connect further devices besides the devices which are already arranged on the CAN bus without having to reconfigure the entire bus.
The document EP 0 895 199 A2 discloses a tachograph connected to numerous further devices by a data bus as cited above. These devices connected to the tachograph by the data bus are able to independently access a printer arranged in the tachograph, i.e. to send data directly to said printer, which data are then printed. In order to allow such actuation of the printer, the control unit of the tachograph must forward data directly intended for the printing unit to said printing unit. Normally, this is accomplished by assigning a bus address to the printer arranged in the tachograph.